1. Field of the Invention
The present disclosure relates to a camera unit which outputs an image signal, and relates to a sensing device including a camera unit which outputs an image signal.
2. Description of the Related Art
An in-vehicle camera which is used in an automotive vehicle is externally attached to the vehicle, and it is required that the in-vehicle camera has a high waterproofing performance although the in-vehicle camera is small in size. A cable needed for the wiring that connects the in-vehicle camera and a display unit internally arranged in the vehicle is almost about 10 m long.
Generally, an automotive vehicle includes several sources of electromagnetic waves, such as an engine and motors. Electromagnetic waves emitted from such sources may affect the in-vehicle camera through the cable, such that noise is superimposed on an image captured by the camera. Conversely, under the influence of electromagnetic waves emitted from the in-vehicle camera, an in-vehicle radio unit may be affected through the cable, such that sound generated by the radio unit becomes noisy. To eliminate the problem, it is important to take measures against electromagnetic interference (EMI) for the in-vehicle camera.
Moreover, it is required that the in-vehicle camera normally operates under severe environmental conditions. When dry conditions are intense, such as in winter, and a user's hand touches the in-vehicle camera, electrostatic discharge occurs frequently. To protect the in-vehicle camera from electrostatic discharge, it is required that the in-vehicle camera has a high resistance to electrostatic discharge.
Japanese Laid-Open Patent Publication No. 2005-347243 discloses an in-vehicle camera in which a circuit board carrying electronic parts, such as a sensor and an image processing circuit, is accommodated in a housing of the in-vehicle camera. If adequate EMI measures are not taken and high voltage due to electrostatic discharge is applied, it may result in malfunction of the in-vehicle camera or destruction of an electronic part. The in-vehicle camera is concerned with the safety performance in vehicle operation, and malfunction of the in-vehicle camera or destruction of the electronic part may significantly affect a human life. Hence, it is required to take adequate EMI measures for the in-vehicle camera.
In the in-vehicle camera according to the related art, a housing made of an insulator, such as a plastic material, is used as the housing of the in-vehicle camera in order to prevent electrostatic discharge from affecting the camera.
Moreover, in the in-vehicle camera according to the related art, when a radiation source of electromagnetic waves exists inside the vehicle, a metal shield plate directly connected to a ground line (GND) of the circuit board is arranged within the housing. As a countermeasure for a case in which electrostatic discharge takes place between a clearance in the insulator and the metal shield plate or the circuit board, the ground line (GND) of the circuit board is connected to a ground line of an external power supply through the cable. This is a known technique.
Japanese Patent No. 3802742 discloses a connector which is used as an in-vehicle component other than an in-vehicle camera. This connector is arranged so that a metal exterior of the connector is enclosed with a metal part connected to a shielding wire of a cable, which causes static electricity to flow through an external ground line to which the cable is connected.
However, the in-vehicle camera according to the related art in which the circuit board is enclosed with the housing of the insulator is directed to preventing occurrence of electrostatic discharge or reducing the occurrence probability of malfunction of the camera or destruction of the electronic part. If no metal shield plate is internally arranged and electrostatic discharge occurs, the portion of the circuit board where the discharge takes place is not predicted. Hence, taking countermeasures or corrective actions requires much time.
Even if a metal shield plate is internally arranged, inside the circuit board, static electricity discharged to the metal shield plate is supplied to the external ground line through the circuit board because the ground line (GND) of the circuit board and the metal shield plate are connected directly at a specific portion. In this case, a high voltage due to the electrostatic discharge is applied to the circuit board instantaneously, and the electronic parts in the circuit board are loaded with this high voltage. Therefore, it is difficult to certainly avoid destruction of the electronic parts due to electrostatic discharge.
Although enclosing the circuit board with the housing of the insulator makes occurrence of electrostatic discharge difficult, once electric discharge occurs, the instantaneous application of a high voltage to the circuit board is unavoidable regardless of the use of a metal shield plate.
A conceivable method for eliminating the problem is to arrange electronic parts which are vulnerable to a high voltage in the areas of the circuit board where the influences of electrostatic discharge are small. However, modification of the circuit board design is not easy to carry out, and it is expected that taking countermeasures or corrective actions requires much time and high cost.
In the connector disclosed in Japanese Patent No. 3802742, the metal exterior and the external ground line are electrically connected. This connector provides a high resistance to electrostatic discharge. However, if this connector is used in an in-vehicle camera, electrical connection between the metal part and the source of electromagnetic waves or the ground line (GND) of the circuit board is not provided, and it is difficult to provide adequate EMI measures.